Mobile electronic devices which have been developed recently may be sometimes intended for use outdoors. Therefore, the housing thereof is required to be made of a lightweight and thin-walled material having high stiffness. For example, Patent Document 1 proposes a carbon fibre reinforced composite material which is lightweight and thin-walled and has a high stiffness and is formed with a sandwich construction comprising two carbon fibre prepregs between which a thermosetting open-cell foam as a core material is laminated.    Patent Document 1: Japanese Patent Application Laid-open No. 2011-093175